The shooting began around 2:30 p.m. at the large school complex located in Broward County in southern Florida. Cruz allegedly pulled the fire alarm to get students out of classrooms and into the hallways. Just that morning, the school had conducted a fire drill.

Many students said they thought they were having another drill Wednesday afternoon when the alarm sounded and most teachers told them to head out of their classrooms.

According to law enforcement authorities, Cruz was waiting outside of the rooms, wearing a gas mask after having set off smoke grenades.

As the students left the rooms, Cruz began firing.

Here’s what we know about Cruz now:

Cruz’s mother died in November. His father had died years earlier.

He and his brother were adopted.

He went to live with a friend’s family after his mother’s death.

A childhood freind of Cruz’s told CNN he would introduce himself as a “school shooter.”

Cruz had been expelled from school.

He legally purchased an AR-15 rifle about a year ago.

He had posted “disturbing” material on social media, according to Israel.

Buzzfeed is reporting that the FBI was warned about a YouTube user named Nikolas Cruz after he posted in September that he was “going to be a professional school shooter.

The Associated Press reported that the leader of a white nationalist group in Florida confirmed Cruz is a member. Later on social media, the leader said there was a misunderstanding and that Cruz was not a member of the group.

The Miami Herald reports that a teacher at the school said Cruz had been identified as a potential threat to fellow students in the past. Math teacher Jim Gard told the Herald, “There were problems with him last year threatening students, and I guess he was asked to leave campus.”

The shooting started outside the building, then Cruz went into the school and continued shooting.

Authorities said he walked out with other students after the shootings.

He had “multiple” ammunition magazines.

He had an AR-15 weapon

He pulled the fire alarm as he went into the school and then began shooting.

After the shooting, he left the campus, went to a Subway located inside of a Walmart where he purchased a drink, then went to a McDonalds where he was arrested without incident.